Fitting members, such as cam lobes and the like, have been assembled on a steel shaft by press-fitting. However, press-fitting is ineffective for fitting members made of sintered alloy. The reason for this is that the hard pre-sintered member easily damages the shaft when forced on the shaft and also the soft green member readily collapses when forced on the shaft. On the other hand, clearance-fitting is shown in JP A No. 54-41266 in which, though the fitting member is loosely fitted on the shaft, it has the projection thereof tightly fitted in the groove in the shaft, because the projection is slightly larger in cross-section than the groove.
The method allows the pre-sintered fitting member to loosely fit on the shaft without damaging the shaft and be fixedly positioned through a fitting engagement between the projection and the groove. However, this method has some disadvantages, one of which is that the fitting member, while sintered at a liquid-phase yielding temperature, sometimes tears from the projection which is tightly retained in the the groove. Another disadvantage of this method is that it is still unavailable for use with the green fitting member, because the projection will break when press-fitted in the groove. Still another disadvantage is that the tight engagement between the projection and the groove sometimes prevents a fully circumferential contact between the bore of the fitting member and the outer periphery of the shaft, thereby failing to achieve a firm connection therebetween.
The present invention is intended to resolve the disadvantages as described above. It will be understood that among the objects of the present invention are: to provide a camshaft in which the projection of the fitting member is prevented from being broken while it is sintered at a liquid-phase yielding temperature, and to provide a camshaft in which the fitting member is fabricated from sinterable alloy powders and fitted on the shaft without being broken. The present invention also provides a camshaft in which the fitting member has a bore thereof which is fully circumferentially bonded to the outer periphery of the shaft except the projection and the groove.